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| Book/Dissertation / PhD Thesis | FZJ-2020-01348 |
2020
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-457-7
Please use a persistent id in citations: http://hdl.handle.net/2128/24507
Abstract: Thermal barrier coatings typically consist of a ceramic top coat on a metallic bondcoat. Used for gas turbine parts, for example the turbine blade, these coatings can protect the blade material from the high temperatures of the combustion gasses, corrosionand oxidation. Besides enhanced top coat bonding, the bond coat ensures oxidation protection of the blade material by oxidising itself. In the present thesis thermally sprayed alumina oxide dispersion strengthened bondcoat materials were produced for the use in thermal barrier coatings. High energy milled bond coat materials were analysed with respect to the material properties and the behaviour in thermal barrier coatings, which were manufactured on single crystal superalloys with a common yttria stabilized zirconia top coat. The bond coats low porosity was achieved by low pressure plasma spraying. For the high porosity of the top coat atmospheric plasma spraying was used. The aging mechanisms of thermal barrier coatings are influenced by several factors. Main factors are stresses in the thermal barrier coating. These stresses arise from the thermal expansion coefficient missmatch between top coat, bond coat, blade material and the oxide layer thermally growing on the bond coat. Previous studies showed a high thermal cycling performance of thermal barrier coatings with double layered bond coats consisting of 2 wt.% alumina oxide dispersion strengthened bond coats on conventional bond coats compared to thermal barrier coatings with single layered conventional bond coats. The approach of this thesis is an increased alumina content up to 30 wt.% in the oxide dispersion strengthened bond coat. The result is a lower thermal expansion coefficient of the upper bond coat reducing the stresses in the thermal barrier coating, which offers a possible increase in thermal barrier coating thermal cycling performance. The approach was proved for thermal barrier coatings using 10% alumina in the oxide dispersion strengthened bond coat. As a result of the lower oxidation resistance of 30% bond coat material, a further increase to 30% alumina does not further improve the thermal cycling performance due to the lower thermal expansion coefficient. Furthermore thermal barrier coatings with columnar structured top coats combined with oxide dispersion strengthened bond coats are promising candidates for high thermal cycling performances. Wear resistant tests showed an increased wear resistance especially for 30% aluminia oxide dispersion strengthened bond coat materials. The research of the present thesis was embedded in the collaborative research center SFB/Transregio 103 “From atoms to turbine blades“ focussing on the developmentof superalloys. Correspondingly single crystal superalloys were used for the thermal barrier coatings [...]
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